Finding an accurate estimate of your BF% is the tricky part.
There are several online calculators based on tape measurements. You can get some calipers. There are some fancy scales that read out BF% with varying degrees of accuracy. And there is the photo method. (Anybody know where that link is to the pics of various BF% examples is?)

The only really accurate way to know BF% is a dunk test but those are expensive and not widely available.